1. Field of Endeavor
The present invention relates to a damper arrangement and a method for designing same.
In particular, in the following reference to a damper arrangement having two or more Helmholtz dampers, connected in series and used to damp pressure oscillations or pulsations that may generate in a combustion chamber of a gas turbine, is made.
2. Brief Description of the Related Art
Gas turbines are known to have one or more combustion chambers, wherein a fuel is injected, mixed to an air flow and combusted, to generate high pressure flue gases that are expanded in a turbine.
During operation, pressure oscillations may generate that could cause mechanical and thermal damage to the combustion chamber and limit the operating regime.
For this reason, usually combustion chambers are provided with damping devices, such as quarter wave tubes, Helmholtz dampers or acoustic screens, to damp these pressure oscillations.
With reference to FIG. 1, traditional Helmholtz dampers 1 include an enclosure 2, that defines a resonator volume 3, and a neck 4 to be connected to a combustion chamber 5, wherein combustion and possibly pressure oscillations to be damped occur (reference 6 indicates the wall of the combustion chamber 5).
The resonance frequency (i.e., the damped frequency) of the Helmholtz damper depends on the geometrical features of the resonator volume 3 and neck 4 and must correspond to the frequency of the pressure oscillations generated in the combustion chamber 5.
In order to address pressure oscillations having different frequencies, two or more Helmholtz dampers are used.
For example, DE 10 2005 062 284 discloses a damper arrangement having two or also more than two Helmholtz dampers connected in series, i.e., the neck of a Helmholtz damper is connected to the volume of another Helmholtz damper. This arrangement proved to be quite efficient in damping pressure oscillation having different, far apart frequencies, such as for example 15 Hz and 90 Hz.
Nevertheless, frequency pressure oscillations may slightly change from gas turbine to gas turbine and, in addition, also for the same gas turbine it may slightly change during gas turbine operation (for example part load, base load, transition).
Since at the low frequency range (where Helmholtz dampers are often used) the damping frequency bandwidth of the Helmholtz dampers is very narrow, such frequency shifting of the pressure oscillations generated in a combustion chamber could render a Helmholtz damper connected to it and having a prefixed design resonance frequency completely useless.
In these cases, traditionally systems for tuning of the resonance frequency are used.
For example, Helmholtz dampers have been developed having an adjustable volume.
WO 2005/059441 discloses a Helmholtz damper having two cup-shaped tubular bodies mounted in a telescopic way.
EP 1158247 discloses a Helmholtz damper whose resonance volume houses a flexible hollow element whose size may be changed by injecting or blowing off a gas; changing the size of the flexible hollow element allows the size of the resonance volume to be changed.
U.S. Patent Application Pub. No. 2005/0103018 discloses a Helmholtz damper whose resonance volume is divided into a fixed and a variable damping volume. The variable volume may be regulated by an adjustable piston.
Alternatively, tuning of the resonance frequency is achieved by adjusting the neck of the Helmholtz dampers.
In this respect, EP 0724684 discloses a Helmholtz damper in which the cross section of the neck may be adjusted.
EP 1624251 discloses a Helmholtz damper with a neck whose length may be adjusted by overlapping a holed plate to its mouth.
All these solutions proved to be quite complex and, in addition, they do not allow a fine tuning of the resonance frequency of the Helmholtz damper, to follow small shifting of the frequency pressure oscillations in the combustion chamber.